What Is a Coupling?
The shaft coupling is a mechanical element that joins two shafts together to accommodate misalignment of torque from one end to the other. In a mechanical system, a coupling can be defined as a type of connection between two rotating shafts that connect the driving and driven shafts together. The joint between two shafts can be permanent or temporary.
In simple words, we can say that couplings are used to connect input and output shafts in any power transmission system like gearbox shaft in machine tools is connected to the input engine shaft through couplings; Engine shaft with pump or compressor shaft, etc.
The function of a coupling is almost the same as that of the clutch, but clutches are temporary joints, whereas coupling joints are permanent connections. The basic purpose of a coupling is to permanently connect two shafts. Shafts in power transmission are not always linear connections; They can be parallel, with intersecting axes and slight eccentricity.
Therefore a different type of Coupling is used in mechanical power transmission. According to the requirement and functions, different types of couplings are used.
The basic characteristics of different types of couplings are almost the same, which are as follows: Power Transmission, Join the misaligned shaft, Reduce tremors and vibrations, Easy to assemble and disassemble.
Shafts can be connected in three ways because generally, in three different ways, shafts are aligned; these are when both shafts are parallel, or we can say that some eccentricity exists between them, collinear shaft and The last one is intersecting the shaft with some angular deflection.
What Is Shaft Coupling?
The shaft coupling is mechanical components that connect two rotating shafts, such as the driving shaft and the driven shaft, for the purpose of transmitting power. It is used in motors, pumps, generators, and compressors. The shaft coupling is a device used to connects two pieces of rotating equipment or shafts for the purpose of transmitting power from one shaft to another.
They are also used for many purposes, common among which are the following:
- To provides for the connection of shafts of separately manufactured units such as motors and gearboxes and to provide for disconnection for repairs.
- To provide for the misalignment of a shaft or to introduce mechanical flexibility.
- To reduce transmission of shock load from one shaft to another.
- To start the protection against overload.
How Does a Shaft Coupling Work?
You can connect two shafts together by Coupling, as shown in the picture above. No problem, shaft diameters are different. According to the above diagram, the motor is the driving side, and the propeller is the driven side.
The Coupling does not transfer the heat etc., of the motor to the driven side. The Coupling absorbs shock and vibration from being moved; this will help prevent damage to surrounding components.
Types of Shaft Coupling:
The different styles & types of shaft coupling are summarized below.
#1. Beam Coupling
Beam couplings have single or multiple helical cuts in the coupling body that can typically accommodate parallel misalignment up to 0.025 inches and angular misalignment up to 7 degrees. They are primarily used for speed control applications where torques are typically below 100 inch-lbs.
Zero backlash designs ensure positioning accuracy between the available driving and driven shafts. The materials used to manufacture beam couplings also affect their performance and suitability for specific applications such as food, medicine, and aerospace.
The materials are typically aluminum alloys and stainless steel, but they can also be made in acetal, marring steel, and titanium. The most common applications for robotics are connecting rotary encoders to shafts and motion controls.
#2. Bellows Coupling
Bellows couplings are also suitable for speed control applications. These consist of multiple convolutions of metal that provide high torsional stiffness, which is important for positioning applications.
Torsional stiffness reduces the level of angular & parallel misalignments they can accommodate compared to beam couplings, although the torque transmission efficiencies are approximately the same. They contain multiple metal fixtures that provide high torsional rigidity, which is important for the application conditions.
Torsional stiffness reduces levels of angular & parallel misalignment that they can accommodate with beam couplings, although the torque transmission capability remains the same.
#3. Chain Coupling
Chain couplings are suitable for power transmission applications and are used to transmit power in the hundreds of horsepower range. Angular & parallel misalignment allowances are typically 2 degrees and 0.015 inches, respectively.
Specialized chain couplings use special chain sprockets and double-wide roller chains whose clearances allow the design to operate as a flexible coupling.
#4. Jaw Coupling
Curved and straight jaw coupling is used for both motion controls and light power transmission applications & consists of pairs of multi-jaw hubs with an elastomeric spider. The design allows for backlash-free torque transmission.
Accommodation for parallel misalignment typically reaches 0.01 inches, and angular misalignment reaches approximately 1 degree. Elastomeric spiders give this Coupling some damping capacity, and often spiders are available in different durometers to attribute specific properties to different couplings.
This Coupling often operates without lubricant and can transmit torque to 1000 in-lb. A jaw coupling is a material flexing coupling that transmits torque through the compression of an elastomeric spider insert placed between two intermeshing jaws.
- The flex element is usually made of NBR, polyurethane, hydrogel, or bronze, Adjusts for misalignment, Transmits torque, Used to reduce torsion (vibration), Low torque, general-purpose applications.
#5. Diaphragm Couplings
The Diaphragm couplings use a single or single series of plates or diaphragms for flexibles members. It transmits torques from the outside diameter of flexibles plates to the inside of the spool or spacer piece and then from the inside to the outside diameter.
Typically they use one or more flexible metal complex discs that transmit power to an internal spacer shaft and then back to the operated machinery via another diaphragm stack.
A major advantage over gear-type couplings is their lack of lubrication requirements. Diaphragm couplings are capable of high torques transmission and high-speed operation.
#6. Disc Coupling
The Disc couplings use single or multiple discs & single or double stages that bolt to the shaft hub. These are used for power transmission and rely on the flexibility of their thin metal discs to transmit torque and accommodate angular misalignment. They are not particularly good at managing parallel misalignment.
These couplings typically include two hubs, two-disc packs, and a center member. A single-disc pack can accommodate angular and axial misalignment. A two-disc pack is required to accommodate parallel misalignment.
- Allows angular parallel and axial deviance, Has a real limited end float design, A zero-feedback design, High-speed rating, and balance.
#7. Oldham Coupling
Oldham couplings handle high levels of parallel misalignment due to their sliding element design. The use of an elastomer center element instead of metal is popular in modern versions. Some manufacturers claim the ability to tolerate 5-degree angular misalignment through the use of cylindrical, rather than rectangular, sliders.
Two discs, typically made of aluminum or stainless steel, are attached to either side of the drive, while the third is one of several different plastics sandwiched between the tongue-and-groove design. Tongue and groove on one side is tongue and groove on the other.
Springs are often used to reduce the backlash of the Coupling. Oldham couplings have several other advantages, including their compact size and the ability for electrical isolation via a plastic center disc.
Can act as fuse for coupling machine. If the torques limit is exceeded, the center discs of the Coupling will break first, thereby avoiding torque transmission and potential damage to more expensive machine components.
#8. Schmidt Coupling
Schmidt couplings are specifically designed to operate on offset shafts. They are not flexible couplings in the strict sense, designed to accommodate minor misalignments in shafts that are theoretically parallel and square to each other.
Schmidt couplings are used in papermaking, printing, & similar machines and act like a 1:1 gearbox in a more compact space.
#9. Bushing Coupling
The bushing flexible coupling is a modification of the rigid coupling type flange coupling. The coupling bolt is known as a pin. Rubber or leather bushings are used over the pin. Also, there is a difference in the texture of the two parts of the Coupling. There is a 5 mm clearances remaining between the faces of the two halve of the Coupling. And there are no rigid connections between them, & the drive is throughs compressed rubber or leather bushings.
#10. Clamping Coupling
Rigid one- and two-piece clamping couplings lack housing for shaft misalignment and are popular for slow or intermittent shafting arrangements where alignment is not a concern. They are the simplest form of shafts coupling and, in addition to lacking misalignment tolerance, are inexpensive zero-backlash devices.
#11. Universal Coupling
Universal Coupling is used to connects two shafts whose axes intersect at a small angle. The bending of two shafts may be constant, but in actual practice, it changes when momentum is transferred from one shaft to another.
The main application of universal or hooks Coupling is found in transmission from the gearbox to the differential or back axle of an automobile. In such a case, we use the Coupling of two hooks, one that connects to the gearbox at one end and the differential at each end of the propeller shaft at the other end.
The Coupling of hooks is also used to transmit power to the various spindles of many drilling machines. It is used as a knees joints in milling machines.
#12. Gear Coupling
The gear coupling transmits the greatest torque and highest amount of torque to the smallest diameter of any flexible coupling. Each Coupling consists of two hubs with large external gear teeth.
Hubs are forged with two internally trimmed sleeves that are bolted together.
Gears couplings accommodate angular & axial misalignment by moving and sliding the crown gear teeth against the mating sleeve teeth. Parallel misalignment is accommodated by two adjacent hub/smooth flex points.
Gear couplings require periodic lubrication depending on the application. They are vulnerable to lubrication failures, but if properly installed and maintained, these couplings have a service life of 3 to 5 years, and in some cases, they can last for decades.
#13. Grid Coupling
The grid coupling consists of 2 radially slotted hubs forged with a serpentine strip of spring steel that allows the grid to bend and flex with the steel strength of the elastomer.
Grid couplings transmit torque from one hub to another through a tapered grid rocking and sliding in parallel mating hub slots and accommodate axial misalignment.
The grid cross-section is generally thinner for better hub contact and easier assembly. As there is movement between the contact hub and the grid metal parts, lubrication is required.
#14. Split Muff Coupling
Splits muff coupling, In this case, the muff or sleeves are made in two halves and bolted together. Half the muff is made of cast iron. The ends of the shafts are designed to be spaced apart, and the same key is fitted directly to the keys of both shafts.
Half of the muff is fixed from below and the other half from above. The two parts are held together using mild steel studs or bolts & nuts. The number of a bolt can be two, four, or six. The nut is recruited in Muff Casting Bodies.
This Coupling can be used for heavy-duty & medium speeds. The advantages of this Coupling are that there is no need to change the position of the shaft for Coupling or assembling.
Application of Couplings:
- Sleeve and Muff Coupling Line shafts in power transmission.
- Clamp or split-muff or compression coupling line shaft in power transmission.
- Flange coupling for alignment accuracy, e.g., Marine.
- Bushed Pin Flexible Coupling Used to connect which have small parallel misalignment, angular misalignment, or axial misalignment. automobile
- Universal Coupling Used to transmit rotary motion or power, e.g., aircraft, driveshafts, etc.
- Oldham’s Coupling Useful in applications where parallel misalignment exists, e.g., Printing Application.